The experimental scenario comprizes two phases of linear colliders. The first phase is well defined at 500GeV. The maximum energy of the second phase is slightly obscure, probably TeV, which must be further investigated, although it depends on the results at the first phase. The competition with the LHC should be emphasized as well as the complementarity for simultaneous experiments and the healthy program of high-energy physics.
Since all forms of background are under control, we can optimize the linac parameters together with the detector designs. Detailed simulations will be needed for each linear collider, including the detectors.
Vertexing based on CCD has proven to be promising. The three-dimensional topological method could clearly reconstruct primary, secondary and tertiary vertices in order to identify u,d,s,c,b and t quarks, ultimately. Active R&D on tracking and calorimetry has also been conducted for JLC-I. New ideas are needed for a compact detector, high magnetic field and particle identification and so on. We expect that many benefits must come from the R&D of the LHC detectors.
New R&D concerning polarized positron beams has been initiated in Japan. This effort should be encouraged in order to significantly strengthen the physics potential for the full ability of linear colliders.
There have been very nice two-dimensional measurements concerning ground motion and modeling at SLAC. It has been demonstrated that ground-motion problems are also under control. The seriousness of culture noise and micro-earthquakes was emphasized. As a result, more studies are needed concerning a fast feedback in linacs, a support system at the interaction region, as well as a consideration of deep underground site for linear colliders.
We thus expect more R&D during the next few years towards the conceptual designs of linear colliders.